The claims involve white slavery, sado-masochism, rapes, sex with minors, drug dealing and appalling brutality - all in the heart of the government of one of France's most historic and most civilised cities. The southern city of Toulouse, known as la ville rose because of its sun-drenched Spanish-style buildings, has been scandalised by allegations that public officials protected a barbaric serial killer charged with murdering prostitutes recruited for orgies in the city's courthouse.

Though the accusations are unproved, Justice Minister Dominique Perben sacked Toulouse's prosecutor-general, Jean Volff, last week for covering up links between senior officials and the exploitation of vulnerable girls. Volff has denied any wrongdoing.

The allegations focus on the activities of Patrice Alègre, a convicted murderer awaiting trial for five other killings. Two former prostitutes have claimed his activities were covered up. A former mayor and three judges have come forward to give their version of events. In a TV appearance, the right-wing former mayor of Toulouse, Dominique Baudis, now head of a broadcasting watchdog, claimed he was being framed by pro-pornography lobbies who wanted to smear him for opposing the showing of X-rated material on national TV.

The three judges have also denied any involvement. They will be questioned about 'acts of torture and barbaric acts, pimping and rapes of under-age girls'.

Detectives have reopened an investigation into the disappearance of 115 young women in the Toulouse area between 1986 and 1997, and are probing earlier claims that Alègre was paid to establish a prostitution network by respected local leaders.

According to press reports, senior police officials covered up Alègre's role as a pimp in Toulouse. The most startling accounts of sexual violence were given by a woman known as Patricia, 32, who went into hiding in 1992 after witnessing two murders.

She has told examining magistrates that Alègre was in charge of recruiting prostitutes and organising orgies. She identified men with whom she had sex at Toulouse's Palais de Justice and said sado-masochist orgies went on at a chateau owned by Toulouse council. She claimed she had witnessed the killing by Alègre of two girls he had recruited.

Another prostitute was allegedly strangled while being raped by Alègre in front of witnesses after she tried to alert police that a vice squad inspector was part of the white slave racket.

The other witness, known as Fanny, was 17 when she was forced into prostitution in 1990 after being recruited by Alègre who, for a time, worked in the police station canteen. She had also witnessed the second murder, but had kept quiet about Alègre's involvement until tracked down two years ago by a gendarmerie squad investigating the unsolved killings of prostitutes in Toulouse and an apparent cover-up by local police.

The appointment of Michel Barrau as prosecutor-general has concerned lawyers because he was credited with stopping an investigation into corruption among senior right-wing politicians in Paris before last year's general election.